Tissue press and system

ABSTRACT

A tissue press for shaping or compressing a piece of tissue comprises first and second members movable relative to each other. A first forming element of a predetermined shape is selectively engageable on the first member. A second forming element of predetermined shape is selectively engageable on the second member. The first and second forming elements are positionable on opposite sides of the piece of tissue. The first and second members are relatively movable between a first spaced apart condition and a second condition in which the piece of tissue is held between the first and second forming elements. Means are preferably provided for monitoring and controlling the amount of pressure applied to the piece of tissue, in order to maintain the tissue in a viable living condition. Means may also be provided for draining off fluid from compressed tissue, so that the tissue can be implanted in a compressed state and imbibe fluid from the host site. A retainer, which may be expandable, can be used to maintain the tissue graft in a compressed condition.

BACKGROUND OF THE INVENTION

Tissue grafting, including bone grafting, is well known. Tissue such asbone is removed from one part of a body (the donor site) and insertedinto tissue in another (the host site) part of the same (or another)body. It is desirable to be able to remove a piece of tissue graftmaterial which is the exact size and shape needed for the host sitewhere it will be implanted. However, it is rarely possible to do this.

Accordingly, various tissue grafting techniques have been tried to solvethis problem. For example, Nashef U.S. Pat. No. 4,678,470 discloses amethod of creating bone graft material by machining a block of bone to aparticular shape, or by pulverizing and milling it. The graft materialis then tanned with glutaraldehyde to sterilize it. This process canproduce bone plugs of a desired shape.

In the Nashef process, the exogenic bone material selected for the graftis presumably dead at the beginning of the process. The process ofpulverizing or milling the bone material destroys the structure of thebone tissue. The step of tanning it with glutaraldehyde then renders thegraft material completely sterile. This condition is not conducive tograft healing and ingrowth. Specifically, applicant has found that it isdesirable to maintain graft tissue in a living state during the graftingprocess. The use of living tissue in a graft will promote bone healing.

SUMMARY OF THE INVENTION

The present invention is a tissue press for shaping or compressing apiece of tissue. The press includes first and second members movablerelative to each other. First and second forming elements of differentpredetermined shapes are positionable on the first and second members onopposite sides of the piece of tissue. The first and second members aremoved toward each other to shape or compress the tissue between thefirst and second forming elements.

Means are preferably provided for monitoring and controlling the amountof force or pressure applied to the piece of tissue, in order tomaintain the tissue in a viable living condition. Means may also beprovided for draining off fluid from compressed tissue, so that thetissue can be implanted in a compressed state and imbibe fluid from thehost site.

The present invention is also a method of reshaping tissue for use asgraft material comprising the steps of determining the shape which thetissue should possess as graft material; providing a tissue press,selecting forming elements adapted to press tissue approximately to thedesired shape, and placing the forming elements on the tissue press;placing the tissue in the tissue press between the forming elements;operating the tissue press to shape the tissue between the formingelements to give the tissue the desired shape; and controlling thepressure on the tissue during the shaping step to minimize damage to ornecrosis of the tissue.

The present invention is also a method which includes the steps ofdetermining the shape and size which the tissue should possess as graftmaterial; placing the tissue in a tissue press having forming elementsadapted to press tissue approximately to the shape and size desired;compressing the tissue in the tissue press to give the tissue the shapeand size desired; controlling the pressure on the tissue during thecompressing step to minimize damage to or necrosis of the tissue; anddraining off fluid expressed during the compressing step.

In accordance with another feature of the present invention, a retaineris provided for retaining tissue graft material in its compressed state.The retainer is placed around the compressed graft. The retainer canhelp to maintain the graft in a compressed configuration or in aspecific shape for a period of time long enough to be placed in thebody. The retainer may be made of a material which expands after it isplaced in the body, to mechanically interlock the graft to the body.

GENERAL DESCRIPTION OF THE INVENTION

With the apparatus and method of the present invention, bone or othertissue can be compressed or reshaped or both, while preserving thetissue alive.

RESHAPING

Often, reshaping of graft tissue is necessary to obtain the bestpossible graft. For example, in an anterior cruciate ligamentreconstruction, the graft material which is removed usually has atriangular cross-sectional configuration. This graft material is placedin an opening in bone formed by drilling with a round drill. When thetriangular graft material is placed in the round opening, there isminimal physical contact between the graft material and the surroundingbone. This reduces the holding power of the graft and also reduces theingrowth ability of the graft.

Thus, an important feature of the present invention is that bone orother tissue such as ligament is reshaped while still leaving it in awhole condition and without substantial tissue damage. The tissue isplaced in the tissue press of the present invention and sufficient forceis applied to reshape the tissue to the desired shape--for example, acylindrical shape as needed for an anterior cruciate ligamentreconstruction. Excessive pressure on the tissue, which can damage orkill the tissue, is avoided as described below. A properly shaped graftis thus provided which is still in a living condition.

Compression

Compression of graft tissue is also sometimes desirable. Generally,tissue is stronger when it is more dense. Compressing graft tissueincreases its density and thus strengthens the graft tissue. The grafttissue also stays together better.

For example, a tendon is made of a plurality of fibers. The individualfibers are weak when separated or unraveled. If a tendon graft isimplanted with the fibers in a loose condition, the graft is weak. Onthe other hand, if prior to implantation the tendon graft is compressedto orient and pack the fibers tightly, then the entire group of fibersacts as one whole unit and the graft is much stronger. Therefore,compressing the tendon graft gives it more mechanical integrity--makinga smaller tendon graft much stronger.

Similarly, bone tissue is stronger and better able to bear force when itis denser and more compact. Compressing bone graft tissue prior toimplantation produces a stronger graft.

Compression of bone or other tissue also allows a surgeon to convert alarger irregular shape into a smaller specific shape. Thus, the surgeonwhen removing the graft material from the donor Site is not limited bythe conditions at the host site but can remove the graft material in thebest way possible from the donor site. Similarly, the surgeon whenimplanting the graft material at the host site is not limited by theshape of the material removed (as dictated by the conditions at thedonor site) but can implant the graft material in the best way possibleto fit the conditions at the host site.

The anterior cruciate ligament, for example, attaches to the femur andtibia at specific isometric locations. When the ligament is beingreplaced in an anterior cruciate ligament reconstruction, typicaluncompressed graft material can be many times the size of thoselocations. In such a case it is necessary to drill openings much largerthan desired in the bone to attach the new ligament. The graft tendonthen tends to fall eccentrically in this larger opening, the functionalanatomy of the ligament can not be recreated, and the functioning of theknee joint is compromised.

However, if the graft material for the new ligament is compressed inaccordance with the present invention, its size can be reducedsubstantially. This allows the surgeon to drill a substantially smalleropening in the bone to attach the new ligament/graft structure, so as torecreate the functional anatomy of the ligament.

With the present invention, it is also possible to make a compositegraft. For example, the graft material for an anterior cruciate ligamentreconstruction is preferably tendon in the middle with bone at bothends. In accordance with the apparatus and method of the presentinvention, bone tissue can be compressed around the ends of tendontissue to form a substitute anterior cruciate ligament more closelyapproximating the original.

It should also be noted that tissues other than bone and tendon can beworked with the tissue press. For example, a surgeon can harvest livercells or pancreas cells and then compress them into a particular shape.They can then optionally be placed into a sack or some type ofstructural support which can be introduced into the body.

With the present invention, graft material can be formed into almost anyshape. A specific pair of forming (mold) parts, having a desiredpredetermined shape, are positioned on the tissue press, and the tissueis shaped or compressed between the forming elements. In addition tothree-dimensional shaped parts, it is also possible to make a flat pieceof graft material. For example, shaved skin can be placed on a flatplate, perhaps on a retaining mesh. The cells are then subjected topressure to adhere them together. A flat, even, piece of graft materialis formed which is suitable for skin grafting.

Compressing graft material in accordance with the present invention alsoallows the surgeon to build up a larger piece of graft material out ofseveral smaller parts. Sometimes a relatively large piece of graftmaterial is needed for a particular host site. It is often not feasibleto take such a large piece of graft material without damaging the donorarea. To avoid this problem, several smaller pieces of graft materialare placed in the tissue press and pressure is used to at leasttemporarily form the smaller parts together as one larger whole. Thelarger graft piece is then inserted into the host site.

Compressing graft material in accordance with the present invention alsoaids in introducing additional materials to the graft material. Theseadditional materials could be antibiotics, bone growth enhancers,tri-calcium phosphate, fibrin, allograft or autograft material, etc.When added to the graft material under pressure, the added materialsadhere to and become a part of the graft material and not merelysomething added to the surface of it. By combining physiologic solutionsor a carrier such as a gelatin, polysaccharides, antibiotics orsynthetic bone materials to the compressed bone, for example, it ispossible to create a plug of living bone with the other materials addedinto it. This plug has the graft properties of the bone tissue in theplug, as well as the properties of the added material.

When tissue is compressed, fluid may be forced out of (expressed from)the tissue. If tissue in this compressed and defluidized state is laidback in a tissue pouch or in a bone hole, body fluids from the host siteare absorbed by the graft material. This imbibition causes swelling ofthe graft material and thus creates a mechanical interlock between thegraft and the host. Such a mechanical interlock is not produced with atypical implantation process in which graft tissue is not compressed.Further, the swelling (enlarging) of the graft material allows the graftmaterial to fill an opening of any given shape with a perfect fit of thegraft material therein.

Pressure monitoring and controlling

As noted above, applicant has found that it is desirable to maintainbone graft tissue in a living state during the grafting process. It isimportant not to kill tissue used in grafting because the living graftcells provide a superior substrate for grafting and graft viability andimproved tissue healing. There is significantly faster incorporation ofliving tissue than of dead tissue. The cells and the tissue that areimplanted into the body therefore need to be maintained in a viablecondition.

Excess pressure on tissue can cause destruction of the tissue,disorganization of the tissue fibers and irregular mechanical structurewhich can damage the tissue graft. Thus, a feature of the presentinvention is that the pressure or force on the tissue being reshaped orcompressed is monitored and controlled. Pressure can be monitored bysuitable pressure sensors and readouts such as a pressure gauge.Pressure can be controlled by force limiting means such as a torquewrench or similar device.

The desired pressure levels may vary. For example, it may be desirableto provide a higher compressive force for cortical bone than forcancellous bone. Similarly, it may be desirable to provide a highercompressive force for bone than for tendon tissue. The appropriate levelof pressure or force is selectively available with the tissue press.

Retainers

A separate device or structure can be used to maintain graft tissue inthe compressed state prior to and during implantation. This separatedevice or structure can be a mesh sack, a ring around a cylindricallyshaped graft material, etc. This additional retainer structure canassist the surgeon in introducing the graft tissue into the body in thecompacted condition, to provide a denser stronger graft and to allowimbibition for creating a mechanical interlock. The retainer can be madeof a material which expands when placed in the body, to provide amechanical interlock for the graft tissue.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other features of the present invention will becomeapparent to one skilled in the art upon a consideration of the followingdescription of the invention with reference to the accompanyingdrawings, wherein:

FIG. 1 is a top plan view of a tissue press embodying the presentinvention;

FIG. 2 is a top plan view of a tissue press similar to the tissue pressof FIG. 1 and having a pressure sensing and monitoring mechanism;

FIG. 3 is an elevational view of the tissue press of FIG. 2;

FIGS. 3A and 3B illustrate a tissue press having means for removingexcess tissue after compression;

FIG. 4A-4F illustrate a plurality of different forming elements for usein the tissue press of FIGS. 1-3;

FIG. 5 is a view of a tissue press in accordance with a secondembodiment of the invention;

FIG. 6 is a view of a tissue press in accordance with a third embodimentof the invention;

FIG. 6A illustrates a tissue press having means for limiting the amountof pressure applied to the tissue;

FIGS. 7 and 7A illustrate a composite tissue graft such as compressionof bone around tendon;

FIG. 8 is a view of a tissue press in accordance with a fourthembodiment of the invention illustrating extrusion of tissue graftmaterial;

FIGS. 9A-9F illustrates a plurality of different retainers forcompressed tissue;

FIGS. 10A and 10B illustrate an expanding tissue retainer;

FIGS. 11, 11A and 11B illustrate an expanding surgical implant; and

FIGS. 12 and 12A illustrate expanding surgical stabilization devices.

DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

The present invention relates to a tissue press and particularly to atissue press for shaping or compressing bone or other tissue. Thepresent invention is applicable to various constructions of tissueshaping or compressing apparatus. As representative of the presentinvention, FIG. 1 illustrates a tissue press 10.

The tissue press 10 includes a base 12. The base 12 has a supportsurface 14 for supporting the base 10 and thus the press 10 on a tableor other support (not shown). The base 12 has the same longitudinalcross-section throughout its width as is seen in elevation in FIG. 1.Two cylindrical pins 16 protect upwardly from the base 12. A U-shapedsaddle 18 is securedto the base 12 by screws 20. A pin opening 22extends transversely through the saddle 18.

The tissue press 10 also includes a handle 30. The handle 30 has aconnector portion 32 received between the upwardly projecting sideportions of the saddle 18 of the base 12. A pin opening 34 extendstransversely through the connector portion 32 of the handle 30. Theopening 34 is aligned with the opening 22 in the saddle 18. A pivot pin36extends through the pin openings 34 and 22 in the handle 30 and base12, respectively, and pivotally connects the handle 30 to the base 12.

Extending from the connector portion 32 of the handle 30 is aform-supporting portion 40 of the handle 30. A channel 42 is defined onthe lower side of the form-supporting portion 40 between a pair ofchannelsurfaces 44. The channel 42 extends transversely across the widthof the form-supporting portion 40. Extending from the form-supportingportion 40 is a circular portion 46 of the handle 30. The circularportion 46 has a manually engageable surface 48 for the application offorce to the handle 30.

A first forming element 50 is slidably received on the base 12. Thefirst forming element 50 has two vertically extending pin openings 52which receive the pins 16 of the base 12. The first forming element 50has an upper surface 54 which includes a forming surface 56. The formingsurface 56 has a cylindrical surface portion 58. The first formingelement 50 has the same longitudinal cross-section throughout its widthas is seen in elevation in FIG. 1. It should be understood that thefirst forming element 50 can be connected with the base 12 in any othersuitable manner.

A second forming element 60 is slidably received in the channel 42 ofthe handle 30. The second forming element 60 has two projecting edges 62whichengage the channel surfaces 44 of the handle 30. The second formingelement60 has a lower surface 64 which includes a forming surface 66.The forming surface 66 includes a cylindrical surface portion 68. Thesecond forming element 60 has the same longitudinal cross-sectionthroughout its width asis seen in elevation in FIG. 1. It should beunderstood that the second forming element 60 can be connected with thehandle 30 in any other suitable manner.

In operation of the press 10, a pair of forming elements 50 and 60 areselected which when brought together will shape a piece of living tissue70 to the desired shape. For example, the forming elements 50 and 60illustrated in FIG. 1 have cylindrical surface portions which will shapetissue into a cylindrical shape suitable for insertion into a rounddrill hole in bone. The first forming element 50 is slid onto the pins16 on thebase 12. The second forming element 60 is slid into the channel42 in the handle 30. A set screw 72 is tightened to secure the secondforming element 60 to the handle 30.

The piece of tissue 70 to be shaped is placed between the first andsecond forming elements 50 and 60. The tissue 70 is preferablypositioned on the forming surface 56 of the first forming element 50 asillustrated in FIG. 1. The handle 30 is then brought toward the base 12in the direction indicated by the arrow 74, by the application of forceto the handle 30. The forming surface 66 with its cylindrical surfaceportion 68 engages thetissue 70, and forces the tissue 70 against theforming surface 56 with itscylindrical surface portion 58. The tissue 70is thereby formed to the desired shape.

It should be understood that with the tissue press 10, tissue can bereshaped only, or reshaped and compressed. The amount and type of workperformed on the tissue depends on the particular application, and iscontrolled by (i) the particular forming elements selected by theoperatorof the tissue press, and (ii) the amount of pressure or forceapplied to the tissue. For example, the forming elements can be selectedso that theydefine between them a forming chamber having the sameinitial volume as thepiece of tissue to be shaped. In this case, thepiece of tissue is not compressed (that is, reduced in volume), but ismerely reshaped. Alternatively, forming elements can be selected whichwill not merely reshape the piece of tissue but also will compress it,as described above.Because the first and second forming elements 50 and60 are removably received on the base 12 and handle 30, respectively,the surgeon can easily select first and second forming elements 50 and60 to reshape or compress the tissue 70 as desired.

As discussed above, it is important to control the pressure on thetissue in the tissue press 10. There are many ways to do this. Forexample, in the press 80 shown in FIGS. 2 and 3, a second formingelement 84 has an opening 82 which extends between its upper surface 86and its forming surface 88. An opening 90 in the handle 92 is alignedwith and in fluid communication with the opening 82. A pressure monitordevice indicated schematically at 94 is in fluid communication with theopening 90 in the handle 92, and thus with the forming surface 88 on thesecond forming element 84. The pressure monitor device 94 can be anyknown device for displaying pressure, such as a dial readout, a barmovable axially in the openings 82 and 90 in response to fluid pressure,etc. The pressure monitor device 94 displays the pressure at the formingsurface 88 of the second forming element 84. This is the pressureapplied to the tissue being pressed in the press 80. Thus, an operatorof the press 80 can observe this pressure monitor device 94 and limitthe applied force accordingly, in order to avoid tissue damage ornecrosis.

Alternatively, a strain gauge of a known construction, indicatedschematically at 96, can be placed on the forming surface 88 of thesecondforming element 84. Electric wires (not shown) transmit signalsfrom the strain gauge 96 to an electric readout device indicatedschematically at 94. The electric readout indicates electrically thepressure applied to the tissue in the press 80. Again, one can observethis pressure monitor device and limit the amount of force applied, inorder to avoid tissue damage or necrosis. It should be understood thatsimilar ways of monitoring the pressure on the tissue being pressed arethe equivalent andare thus included within the scope of the invention.

Any of the tissue presses of the present invention can include means forcutting off excess tissue. As an example, FIGS. 3A and 3B illustrate atissue press 91 having an independent cutoff arm 93 pivotally mountedadjacent the handle 95. The cutoff arm 93 has a blade portion 97operable to cut off excess tissue compressed by the tissue press 91. Thecutoff arm93 is, of course, merely illustrative of the many equivalentstructures usable to remove excess tissue after the compressing orshaping operation.Thus, the length of the tissue graft material, as wellas its compressed diameter, can be selectively controlled by operationof the tissue press. It should be noted that this cutting off processcan be effected with the edges of the forming elements themselves, asillustrated in the apparatus in FIG. 5.

As noted above, the first forming element 50 and the second formingelement60 are removably received on the base 12 and handle 30,respectively. Thus,forming elements having forming surfaces with othershapes can be easily placed in the tissue press 10, in order to shape orcompress tissue into other shapes. A few of the many shapes obtainableare illustrated in FIG. 4.

FIG. 4A, for example, illustrates the forming elements 50 and 60 ofFIGS. 1-3 which shape tissue into a cylindrical cross-sectional shape.FIG. 4B illustrates forming elements 100 and 102 which shape tissue intoan oblongcross-sectional shape, between a forming surface 104 on thefirst forming element 100 and a forming surface 106 on the secondforming element 102. FIG. 4C illustrates forming elements 108 and 110which shape tissue into asquare cross-sectional shape, between a formingsurface 112 on the first forming element 108 and a forming surface 114on the second forming element 110.

FIG. 4D illustrates forming elements 116 and 118 which shape tissue intoa triangular cross-sectional shape, between a forming surface 120 on thefirst forming element 116 and a forming surface 122 on the secondforming element 118. FIG. 4E illustrates forming elements 124 and 126which shape tissue into a generally flat shape, between a formingsurface 128 on the first forming element 124 and a forming surface 130on the second forming element 126. FIG. 4F illustrates forming elements132 and 134 which shape tissue into a semi-circular cross-sectionalshape, between a forming surface 136 on the first forming element 132and a forming surface 138 on the second forming element 134. Again, itshould be understood that other shapes are conceivable and consequentlyare included within the scope of the invention.

In addition to three-dimensional shaped parts, it is also possible tomake a flat piece of graft material. Forming elements like those shownin FIG. 4E are useful in this case. For example, a skin graft may beplaced on an adhesive based mesh (possibly using fibrin) on the flatforming surface 128. The cells are then subjected to pressure to adherethem together. Thecells are spread out over a finer layer. A flat, even,piece of skin graft material is formed. This can then be cut or pressedor formed into a specific shape and then used as a skin substitute onthe body.

Any forming element useful in the present invention can be coated with anon-stick coating to reduce adhesion of the compressed tissue to theforming elements. For example, the forming element 100 (FIG. 4B) isindicated as having a non-stick coating 105 such as a Teflon® coatingwhich may be applied in any suitable known manner. Such a coating canresist the binding of the tissue (or tissue additive such as fibrindiscussed below) to the forming element. 10 In a second embodiment ofthe invention, illustrated in Fig. 5, a tissue press 150 is fluidoperated (pneumatic or hydraulic) rather than manually operated. Thepress 150 includes a base 152 having a support surface 154 forsupporting the base 152 and thus the press 150 on a table 15 or othersupport (not shown). A first forming element 156 is attached to the base152. The first forming element 156 may be slidably or otherwise attachedto the base 152 in any suitable manner which blocks movement of theforming element 156 relative to the base 152 during operation of 20 thepress 150 and which allows for easy interchange of forming elements 156.The first forming element 156 has an upwardly facing forming surface158. A fluid drain opening 160 is in fluid communication with theforming surface 158 of the first forming element 156.

An air or hydraulic cylinder 170 is fixed to the base 152 above thefirst forming element 156. The cylinder 170 has a port 172 for theintroduction of air or other fluid under pressure to operate a piston174 in a known manner. A second forming element 180 is connected to thepiston 174. The second forming element 180 is attached to the piston 174in any suitable manner which blocks movement of the forming element 180relative to the piston 174 during operation of the press 150 and whichallows for easy interchange of forming elements 180. The second formingelement 180 has a forming surface 182 facing the forming surface 158 onthe first forming element 156.

A port 176 in the cylinder 170 is in fluid communication with theforming surface 182 of the second forming pat 180. Connected to the port176 is a pressure monitor device shown schematically at 178.

In operation of the press 150, a pair of forming elements 156 and 180are selected which when brought together will shape tissue to thedesired shape. The first forming element 156 is attached to the base152. The second forming element 180 is attached to the piston 174. Apiece of tissue to be shaped (not shown) is placed between the first andsecond forming elements 156 and 180. The piece of tissue is preferablypositionedon the forming surface 158 of the first forming element 156.

The cylinder 170 is then actuated to move the second forming element 180toward the first forming element 156. The forming surface 182 on thesecond forming element 180 engages the tissue, and forces the tissueagainst the forming surface 158 on the first forming element 156.Pressureon the tissue is controlled through observation of the monitordevice 178. The tissue is formed to the desired shape. Again, it shouldbe understood that with the press 150 tissue can be reshaped only, orcompressed also, depending on the application, the forming elementsselected, and the amount of force applied.

As discussed above, when tissue is compressed, fluid may be expressedfrom the tissue. In the press 150, the second forming element 180 fitswithin the first forming element 156 to define between them a closedforming chamber in which the tissue is compressed. Expressed fluid isdrained fromthe forming chamber through the fluid drain opening 160. Ifa closed forming chamber is not formed, as for example with theopen-ended forming elements shown in FIGS. 1-4, then expressed fluid candrain outwardly fromthe tissue being pressed, without the need for aseparate fluid drain port.Of course, a separate fluid drain port couldbe provided in any of the forming elements of the present invention.

In a third embodiment of the invention, illustrated in FIG. 6, a tissuepress 200 includes a base 202 having a support surface 204 forsupporting the base 202 and thus the press 200 on a table or othersupport (not shown). A first forming element 206 is attached to the base202. The firstforming element 206 may be slidably or otherwise attachedto the base 202 in any suitable manner. The first forming element 206includes a pluralityof first fingers 208 which together have a formingsurface 210 to progressively compress bone or other tissue into apredetermined shape.

An upper arm 220 is pivotally mounted to the base 202 by a pivot pin222. Asecond forming element 224 is connected to the upper arm 220 in asuitable manner. The second forming element 224 includes a plurality ofsecond fingers 226 which together have a forming surface 228 facing theforming surface 210 on the first forming element 206. The second fingers226 are interdigitable with the first fingers 208.

In operation of the press 200, a pair of forming elements 206 and 224are selected which when brought together will progressively shape tissueto the desired shape. The first forming element 206 is attached to thebase 202. The second forming element 224 is attached to the upper arm220. A piece of tissue to be shaped (not shown) is placed between thefirst and second forming elements 206 and 224. The piece of tissue ispreferably positioned on the forming surface 210 of the first formingelement 206. The upper arm is pivoted toward the base to move the secondforming element 224 toward the first forming element 206. The formingsurface 228 on the second forming element 224 engages the tissue, andforces the tissue against the forming surface 210 on the first formingelement 206. The tissue is formed to the desired shape.

Because the second fingers 226 are interdigitable with the first fingers208, the press 200 is operable to compress tissue to differentcompressed sizes with only one pair of forming elements. As the secondfingers 226 come together with the first fingers 208, they compress thetissue to a smaller and smaller diameter (shape). This allows for onepair of forming elements to provide compression to variable diameters orsizes. This workswell with soft tissue applications, specificallytendons, to compress the tendon into a smaller shape. The amount ofcompression is based on the amount of pressure applied and the neededfinished size.

As noted above, it is important to control the pressure or force appliedtothe tissue by the tissue press. Accordingly, the present inventionprovidesmeans for limiting the amount of pressure applied to the tissueby the tissue press, that is, means for blocking application to thetissue of force in excess of a predetermined amount. Such means areschematically illustrated in FIG. 6A, which illustrates a tissue press300 having a known torque wrench assembly included therein.

The press 300 includes a base 302. Attached to the base in the mannerdescribed above is a first forming part 304. Also attached to the baseis a saddle 306. Received in the saddle 306 is the connector portion 308of ahandle assembly 310. The press 300 also includes a pivot pin 312pivotally interconnecting the handle assembly 310 and the base 302.

The handle assembly 310 includes a form-supporting portion 314 to whichthere is attached in the manner described above a second forming part316.The handle assembly 310 also includes a second portion 318 connectedto theform-supporting portion 314 by a drive mechanism 320. The secondportion 318 includes a knurled section 322 which is rotatable about anaxis 324. On the second portion 318 there is a gauge 326.

The knurled section 322 is rotatable about the axis 324 to set thetorque value desired and as shown on the gauge 326. Thereafter, thehandle assembly 310 can be pivoted toward the base 302 in the directionindicatedby the arrow 328 only until the preset amount of torque isapplied. At thatpoint, no more torque is transferred through the drivemechanism 320 to theform-supporting portion 314. This limits the amountof pressure applied to the tissue by the second forming part 316, thatis, blocks application to the tissue of force in excess of apredetermined amount.

It should be understood that the torque wrench assembly or constructionindicated in FIG. 6A is only illustrative of the many ways in which theamount of pressure applied to the tissue by the tissue press can belimited to a predetermined amount. There are other known mechanisms forperforming the same function, and their use is included within the scopeof the present invention.

FIGS. 7 and 7A illustrate the use of a tissue press in accordance withthe present invention to form a composite graft. As discussed above,with the present invention, it is also possible to make a compositegraft. For example, the graft material for an anterior cruciate ligamentreconstruction is preferably tendon in the middle with bone at bothends. In accordance with the apparatus and method of the presentinvention, bonetissue can be compressed around the ends of tendon tissueto form a substitute anterior cruciate ligament more closelyapproximating the original.

Thus, as illustrated schematically in FIGS. 7 and 7A, the tissue press10 of FIGS. 1-4 is being used to compress bone tissue 240 around tendontissue 242 to form a substitute anterior cruciate ligament 244. Thetendon242 can be harvested from one site and the bone 240 can beharvested from another site.

It should be understood that the graft can be multiple tissue fragmentsrather than a composite material. Thus, the tissue press 10, or indeedanytissue press in accordance with the present invention, can be used tocompress, for example, multiple bone fragments into one larger piece. Itshould also be understood that the tissue press in accordance with thepresent invention can be used to add additional materials to body tissuematerial by pressure. For example, to bone tissue there can be addedtri-calcium phosphate, an antibiotic, hydroxyapatite, allografts orautografts, or any other polymeric. This process is believed to beself-explanatory in light of the foregoing description, but forreference may be understood by referring to FIGS. 7 and 7A wherein 240would be the bone tissue or other tissue to which material is beingadded (squeezed in under pressure), and 242 indicates the additionalmaterial being added to the tissue 240.

In this case, fibrin can be highly suitable for use as such anadditional material. Fibrin is a blood component important in bloodclotting. It can be separated or centrifuged from blood and has thenature of an adhesive gel. Fibrin can be used as an adhesive, either ina natural state or afterbeing compressed, to hold together material suchas separate tissue pieces pressed together in a tissue press of thepresent invention.

In a fourth embodiment of the invention, illustrated in FIG. 8, a tissuepress 250 is operated to extrude rather than press material. The press250includes a base 252 having a support surface 254 for supporting thebase 252 and thus the press 250 on a table or other support (not shown).A die 256 is attached to the base 252. The die 256 may be slidably orotherwise attached to the base 252 in any suitable manner which blocksmovement of the die 256 relative to the base 252 during operation of thepress 250 andwhich allows for easy interchange of forming elements 256.The die 256 has an upwardly facing opening 258. An extrusion opening 260is in fluid communication with the opening 258 of the die 256.

An air or hydraulic cylinder 270 is fixed to the base 252 above the die156. The cylinder 270 has a port 272 for the introduction of air orother fluid under pressure to operate a piston 274 in a known manner. Aram 280 is connected to the piston 274. The ram 280 has a surface 282facing the opening 258 on the die 256.

In operation of the press 250, a die 256 is selected which will extrudetissue in the desired shape. The die 256 is attached to the base 252. Apiece of tissue to be extruded (not shown) is placed in the opening 258ofthe die 256. The cylinder 270 is then actuated to move the ram 280toward the die 256. The surface 282 on the ram 280 engages the tissue,and forcesthe tissue into and through the die 256, exiting through theopening 260. The tissue is extruded in the desired shape. As discussedabove, a fluid drain port can be provided in the press 250.

It can also be useful to heat or cool the tissue being worked in atissue press of the present invention. Accordingly, the presentinvention contemplates the use of means for selectively controlling thetemperature of the piece of tissue while it is being compressed orshaped. As an example, illustrated schematically in FIG. 4 is a fluidpassage 284 extending from the outer surface of the forming element 124and around theforming surface 128 thereof. Fluid which is either heatedor cooled flows through the passage 284 and either cools or heats thematerial of the forming element 124 in the area adjacent the formingsurface 128. Thus, the tissue, when it comes in contact with the formingsurface 128, can be selectively heated or cooled during the compressionor reshaping operation. Heating can be useful in holding togethermaterials being compressed, for example, and cooling can be useful toavoid tissue damage arising from overheating of tissue being compressed.It should be understood that other means of achieving these functionsare contemplated,such as electrical heating elements. Further, bothforming elements can be heated or cooled rather than just one. Any suchequivalent structure is tobe considered within the scope of the presentinvention.

In accordance with another feature of the present invention, a retaineris provided for retaining tissue graft material in its compressed state.After the graft is compressed, the retainer is placed around the graft.The retainer can help to maintain the graft in a compressedconfiguration or in a specific shape for a period of time long enough tobe placed in the body.

The retainer may be one of many different shapes. The shape of theretaineris chosen to meet the specific application. There are a numberof suitable shapes, such as a ring, a cylinder, a cage, a rectangularshape, a mesh, asuture-like wrap, etc. Some of these are illustratedschematically in FIGS.9A-9F. It should be understood that this is not anexhaustive listing, but rather that these are merely exemplary of theprinciple involved, and accordingly, the invention is not limited tothese particular shapes. For example, a retainer may be provided whichis in the particular shape of the tissue material being compressed,which can be rectangular, cylindrical, planar, etc.

FIG. 9A illustrates a plurality of bands or rings 290 used to holdtogethercompressed tissue 292. FIG. 9B illustrates a cage 294 which canbe used to hold together the compressed tissue 292 of FIG. 9A. The cage294 includes a plurality of crossed filaments 296 which define betweenthem a series ofopenings 298 for tissue ingrowth. FIG. 9C illustratesanother cage 300 which can be used to hold together the compressedtissue 292 of FIG. 9A. The cage 300 includes a plurality oflongitudinally extending filaments 302 which define between them aseries of openings 304 for tissue ingrowth. FIG. 9D illustrates asolid-walled cylinder 306 which can be used to hold together thecompressed tissue 292. FIG. 9E illustrates a mesh cylinder 308 which canbe used to hold together the compressed tissue292. FIG. 9F illustratesthe wrapping of a cord or suture 310 around compressed tissue 312.

Any of these retainers may be made of various materials. The material ofthe retainer is chosen to meet the specific application,. Some of themanymaterials which are suitable are biodegradable materials, ceramics(especially with bone-growth enhancers, hydroxyapatite, etc.); polymericmaterial such as Dacron or other known surgical plastics; metal; orcomposite materials.

In use, the graft material may be pushed into the retainer structureafter graft material is compressed. Alternatively, the graft materialmay be compressed with the retainer structure. After the graft materialis compressed in the retainer, the combined structure of graft plusretainer is placed in the host site in the body. The retainer helps tomaintain thegraft in a compressed configuration or in the specific shapeinto which it was compressed for a period of time long enough to beplaced in the body.

If the retainer is made of a biodegradable material, then the retainerdegrades and disappears after a period of time. If the retainer is notmade of a biodegradable material, then the retainer remains in the body.Tissue ingrowth occurs to bind the host tissue to the graft material.Tissue ingrowth through and around the retainer, between the host tissueand the graft material, is promoted if there are openings as discussedabove in the retainer.

The invention, the retainer may, if desired, be made of a material whichexpands after it is placed in the body, to mechanically interlock thegraft to the body. The expansion can take place in one of two ways.First,the retainer can itself be compressed, as with the tissue, thenexpand whenplaced in the body. Second, the retainer can be made of amaterial which expands when it comes in contact with water or otherbodily fluids.

(It should be noted that the tissue can itself be compressed then expandwhen contacted by water. As an example, a tendon can be compressed in adesiccated state, and as it imbibes water it expands and creates afirmer lock or tighter fit in the host site.)

The expandable material can first be compressed with the tissue beinggrafted, and which then expands when placed in the body. The retainer ispreferably made of a material which has more structural stability thanthetissue being grafted, and provides mechanical integrity andstructural support for the graft tissue. A retainer made of a solidpolymeric material, for example, is useful to retain in a compressedstate a tendon or bone tissue graft.

These expandable materials can be used not only to retain graftmaterial, but for any shape required for stabilization surgery, such asa wedge, screw, rivet, retaining ring, or spacer, an intramedullary rod,a joint replacement part such as a femoral component of acetabular cup,an expandable sleeve, or another mechanical structure. The expandablematerials thus can be used both as a carrier or retainer for anothermaterial (e.g. tissue graft material) and on their own as a prostheticelement.

There are a number of suitable materials which expand when they come incontact with water or other fluids. One is PEEK (polyether-etherketone).Adesiccated biodegradable material, or a desiccated allograft may alsobe

As a simple example, an expandable retainer 330 (FIG. 10) with grafttissue332 therein is placed into a tissue or bone space 334 defined byan edge 336 in host tissue 38. As the retainer 330 imbibes body fluidsor water from the host tissue 338, it expands radially outwardly intothe tissue orbone space 334 and creates a mechanical interlock (FIG.10A). It also expands radially inwardly and clamps on the graft tissue332. Therefore, the graft tissue 332 is locked into the host site,without the necessity of damaging the tissue further through some otherkind of attachment means.

For example, a hip replacement (femoral head) is typically made ofmetal. To implant the replacement, the softer, inner cancellous bone ofthe femuris first removed. The inner surface of the cortical bone isthen machined to provide a close fit between the external surface of thereplacement andthe hard outer cortical bone material. All this requiresa substantial opening in the femur and still does not guarantee a closeenough fit for the implant.

If, instead, the implant is made of an expanding material such as PEEK,only a smaller opening is needed, thus reducing trauma to the bone.Although it is best to lock against the cortical bone, it is possible toimplant solely in the cancellous bone, which because of the expansion ofthe implant provides a better fit than a metal implant. A benefit ofimplanting in the cancellous bone is reduction of the danger of puttingthe implant in so tightly that the cortical bone is split (wedged open).Further, if the opening in the bone is not exactly the same shape as theouter surface of the implant, the implant expands to provide a customcontoured fit to the bone and provide immediate mechanical stability.Thus, less machining of the bone is needed, while at the same timeobtaining a closer fit.

Thus, as illustrated in FIG. 11-11B, a hip replacement (femoral head)340 is made of PEEK or another expandable material. The replacement 340is inserted into an intramedullary channel 342 cut into a femur 344. Thereplacement 340 is smaller in diameter than the channel 342. Thereplacement 340 absorbs body fluids and expands to lock itself into thechannel 342 in the femur 344. (It should be understood that the scaleshown in FIGS. 11-11B is exaggerated as to the amount by which thereplacement 340 expands.)

Similarly, a bone plate or other structure or tissue can be secured to abone with a fastener made of such an expandable material. As illustratedschematically in Figs. 12 and 12A, a bone plate 350 is secured to a bone352. In FIG. 12, a fastener 354 is used which has an unthreaded portion356 extending into the bone 352. The fastener 354, or at least theunthreaded portion 356, is made of PEEK or another suitable expandablematerial. The portion 356 imbibes fluid from the bone 352 and expandsradially outwardly, from an unexpanded condition as shown in phantom at358 to an expanded condition as shown in solid lines at 360, to lock thefastener 354 into the bone 352. This enables the securing of the plate350to the bone 352 without cutting threads into the bone 352 as isusually done.

In FIG. 12A, a fastener 362 has a threaded portion 364 extending intothe bone 352. The threaded portion 364 is made of PEEK or anothersuitable expandable material. The threaded portion 364 imbibes fluidfrom the bone 352 and expands radially outwardly to additionally lockthe fastener 362 into the bone 352. Alternatively, the fastener 362 ofFIG. 12A may have a coating 366 on its portion threaded into the bone352. The coating 366 is made of PEEK or another suitable expandablematerial. The coating 366 imbibes fluid from the bone 352 and expandsradially outwardly to additionally lock the fastener into the bone 352.

When such a fastener is made of a non-metal expandable material, removalofthe fastener simply entails drilling out the center thereof. This ismuch easier than with a typical metal bone screw.

From the above description of the invention, those skilled in the artwill perceive improvements, changes and modifications. Suchimprovements, changes and modifications within the skill of the art areintended to be covered by the appended claims.

I claim:
 1. A tissue press for compressing or shaping a piece of tissue,comprising:a first member, and a first forming element on said firstmember; a second member connected with said first member, and a secondforming element on said second member; said second member being movabletoward said first member to move said second forming element toward saidfirst forming element to compress or shape the piece of tissue betweenthe first and second forming elements; and means for selectivelycontrolling the temperature of the piece of tissue while it is beingcompressed or shaped.
 2. A tissue press as set forth in claim 1 whereinsaid means for selectively controlling the temperature of the piece oftissue comprises means for heating the piece of tissue.
 3. A tissuepress as set forth in claim 1 wherein said means for selectivelycontrolling the temperature of the piece of tissue comprises means forcooling the piece of tissue.
 4. Apparatus for shaping a piece of tissue,comprising:first and second relatively movable members; a plurality offirst forming elements of different predetermined shapes selectivelyengageable on said first member; means for connecting a selected one ofsaid first forming elements with said first member; a plurality ofsecond forming elements of different predetermined shapes selectivelyengageable on said second member; means for connecting a selected one ofsaid second forming elements with said second member; said first andsecond forming elements when connected with said first and secondmembers being positionable on opposite sides of the piece of tissue; andsaid first and second members being relatively movable between a firstspaced apart condition and a second condition in which said piece oftissue is shaped between said first and second forming elements; whereinsaid first and second forming elements include surface means for shapingthe tissue into a square shape.
 5. Apparatus for shaping a piece oftissue, comprising:first and second relatively movable members; aplurality of first forming elements of different predetermined shapesselectively engageable on said first member; means for connecting aselected one of said first forming elements with said first member; aplurality of second forming elements of different predetermined shapesselectively engageable on said second member; means for connecting aselected one of said second forming elements with said second member;said first and second forming elements when connected with said firstand second members being positionable on opposite sides of the piece oftissue; and said first and second members being relatively movablebetween a first spaced apart condition and a second condition in whichsaid piece of tissue is shaped between said first and second formingelements; wherein said first and second forming elements include surfacemeans for shaping the tissue onto a triangular shape.
 6. Apparatus forshaping a piece of tissue, comprising:first and second relativelymovable members; a plurality of first forming elements of differentpredetermined shapes selectively engageable on said first member; meansfor connecting a selected one of said first forming elements with saidfirst member; a plurality of second forming elements of differentpredetermined shapes selectively engageable on said second member; meansfor connecting a selected one of said second forming elements with saidsecond member; said first and second forming elements when connectedwith said first and second members being positionable on opposite sidesof the piece of tissue; and said first and second members beingrelatively movable between a first spaced apart condition and a secondcondition in which said piece of tissue is shaped between said first andsecond forming elements; wherein said first and second forming elementsinclude surface means for shaping the tissue into a semicircular shape.7. A tissue press for compressing a piece of tissue, comprising:a basemember; a first compressing part on said base member for receiving thepiece of tissue thereon; a movable member connected with said basemember and movable relative to said base member; a second compressingpart on said movable member, said first and second compressing partsbeing positionable on opposite sides of the piece of tissue when thepiece of tissue is received on said first compressing part; said movablemember being movable toward said base member to move said secondcompressing part toward said first compressing part to compress thepiece of tissue between the first and second compressing parts, saidbase member including surface means for supporting said base member andthereby said apparatus on an external support surface, said movablemember being pivotally supported by said base member; and means forselectively controlling the temperature of the piece of tissue while itis being compressed.
 8. A tissue press for reshaping a piece of humantissue to a particular overall shape without substantially changing thetexture or consistency of the tissue, comprising:first and secondrelatively movable members connected with each other for relativemovement; said first member having a first forming surface of a firstpredetermined shape for providing a first portion of the overall shapeof the reshaped tissue, said second member having a second formingsurface of a second predetermined shape for providing a second portionof the overall shape of the reshaped tissue, said first and secondforming elements being positionable on opposite sides of the piece oftissue to be shaped, and actuator means for connecting said first andsecond relatively movable members for relative movement of said secondforming element toward said first forming element with the tissue piecebetween them to reshape the tissue piece between the first and secondforming surfaces without substantially changing its texture orconsistency, said first member has a surface portion receiving aselected one of a plurality different of easily removable,interchangeable first forming elements of different predeterminedshapes, said first forming element having said first forming surface,said second member having a surface portion receiving a selected one ofa plurality of easily removable, interchangeable second forming elementsof different predetermined shapes, said second forming element havingsaid second forming surface.
 9. A tissue press for reshaping a piece ofhuman tissue to a particular overall shape without substantiallychanging the texture or consistency of the tissue, comprising:first andsecond relatively movable members connected with each other for relativemovement; said first member having a first forming surface of a firstpredetermined shape for providing a first portion of the overall shapeof the reshaped tissue; said second member having a second formingsurface of a second predetermined shape for providing a second portionof the overall shape of the reshaped tissue; said first and secondforming elements being positionable on opposite sides of the piece oftissue to be shaped; actuator means for connecting said first and secondrelatively movable members for relative movement of said second formingelement toward said first forming element with the tissue piece betweenthem to reshape the tissue piece between the first and second formingsurfaces without substantially changing its texture or consistency; andmeans for selectively controlling the temperature of the piece of tissuewhile it is being compressed.
 10. A tissue press for compressing a pieceof human tissue to a smaller volume without substantially changing itsconstitution, form, or texture, comprising:first and second relativelymovable members connected with each other for relative movement; saidfirst member having a first forming surface at least partially defininga first predetermined volume for providing a first portion of theoverall shape of the reshaped tissue; said second member having a secondforming surface at least partially defining a second predeterminedvolume for providing a second portion of the overall shape of thereshaped tissue; said first and second forming elements beingpositionable on opposite sides of the piece of tissue to be shaped; andactuator means for connecting said first and second relatively movablemembers for relative movement of said second forming element toward saidfirst forming element with the tissue piece between them to compress thetissue piece to a smaller volume without substantially changing itsconstitution, form, or texture; said first member has a surface portionreceiving a selected one of a plurality of easily removable,interchangeable first forming elements of different predeterminedshapes, said first forming element having said first forming surface;said second member having a surface portion receiving a selected one ofa plurality of easily removable, interchangeable second forming elementsof different predetermined shapes, said second forming element havingsaid second forming surface.
 11. A tissue press as defined in claim 7comprising means for draining off fluid which may be expressed from thepiece of tissue.
 12. A tissue press as defined in claim 11 wherein saidfirst and second compressing parts each include a cylindrical surfaceportion and said first and second forming elements cooperate to compresstissue into a cylindrical shape.
 13. A tissue press as defined in claim7 comprising means for monitoring the amount of pressure applied to thepiece of tissue.
 14. A tissue press as defined in claim 13 wherein saidmeans for monitoring pressure comprises a pressure sensor in one of saidfirst and second compressing parts for sensing the amount of pressure onthe piece of tissue.
 15. A tissue press as defined in claim 13 whereinsaid means for monitoring pressure comprises display means fordisplaying the amount of pressure applied by said first and secondcompressing parts.
 16. A tissue press as set forth in claim 7 whereinsaid means for selectively controlling the temperature of the piece oftissue comprises means for heating the piece of tissue.
 17. A tissuepress as set forth in claim 7 wherein said means for selectivelycontrolling the temperature of the piece of tissue comprises means forcooling the piece of tissue.
 18. A tissue press as defined in claim 7further including means for selectively removing excess tissue from thepiece of tissue after it is compressed.
 19. A tissue press as defined inclaim 7 further including a non-stick coating on at least one of saidfirst and second forming elements to limit adhesion of the piece oftissue while it is being compressed.
 20. A tissue press as defined inclaim 7 comprising means for limiting the amount of pressure applied tothe piece of tissue.
 21. A tissue press as defined in claim 1 comprisingmeans for draining off fluid which may be expressed from the piece oftissue during pressing.
 22. A tissue press as defined in claim 1 whereinsaid first and second forming elements each include a cylindricalsurface portion and said first and second forming elements cooperate tocompress tissue into a cylindrical shape.
 23. A tissue press as definedin claim 1 comprising means for monitoring the amount of pressureapplied to the piece of tissue.
 24. A tissue press as defined in claim23 wherein said means for monitoring pressure comprises a pressuresensor in one of said first and second forming elements for sensing theamount of pressure on the piece of tissue.
 25. A tissue press as definedin claim 23 wherein said means for monitoring pressure comprises displaymeans for displaying the amount of pressure applied by said first andsecond forming elements.
 26. A tissue press as defined in claim 1further including means for selectively removing excess tissue from thepiece of tissue after it is pressed.
 27. A tissue press as defined inclaim 1 further including a non-stick coating on at least one of saidfirst and second forming element to limit adhesion of the piece oftissue while it is being compressed.
 28. A tissue press as defined inclaim 1 comprising means for limiting the amount of pressure applied tothe piece of tissue.
 29. A tissue press as set forth in claim 9,including limiting means for limiting movement of said first and secondforming surfaces toward each other when said first and second formingsurfaces are spaced from each other by a predetermined distance, saidfirst and second forming surfaces then defining between them a reshapingcavity having a predetermined volume, for reshaping the tissue piecewithout substantially changing its volume.
 30. A tissue press as setforth in claim 9 wherein said actuator means for connecting includes apivot connection interconnecting said first and second relativelymovable members on one side of said first and second relatively members,said tissue press including a handle on one of said first and secondrelatively members, said handle being spaced from said first and secondforming elements on a side of said tissue press opposite from said pivotconnection.
 31. A tissue press as defined in claim 9 wherein said firstand second forming elements each include a cylindrical surface portionand said first and second forming elements cooperate to compress tissueinto a cylindrical shape.
 32. A tissue press as defined in claim 9comprising means for monitoring the amount of pressure applied to thepiece of tissue, comprising a pressure sensor in one of said first andsecond forming elements for sensing the amount of pressure on the pieceof tissue.
 33. A tissue press as defined in claim 9 further includingmeans for selectively removing excess tissue from the piece of tissueafter it is compressed.
 34. A tissue press as defined in claim 9 furtherincluding a non-stick coating on at least one of said first and secondforming elements to limit adhesion of the piece of tissue while it isbeing compressed.
 35. A tissue press as set forth in claim 10 includinglimiting means for blocking movement of said first and second formingsurfaces toward each other when said first and second forming surfacesare spaced from each other by a predetermined distance, said first andsecond forming surfaces then defining between them a compressing cavityhaving a predetermined volume, for compressing the tissue piece withoutsubstantially changing its constitution, form, or texture.